Method and apparatus for diffusive transfer between immiscible fluids

A method of carrying out a process of diffusive transfer of an entity from a first fluid to a second fluid immiscible with the first, the method comprising the steps of:

• providing a foraminous sheet means having apertures and, on opposite sides and first and second flow paths communicating with one another across said foraminous sheet means having apertures, a height of each of the apertures in the sheet means being no more than 200 micrometers as measured at an interface position in a direction perpendicular both to a direction of fluid flow and to a width of the sheet means, each aperture being formed to permit fluid to flow into the aperture without interfering with fluid flow out of the aperture,
• flowing the first and second fluids through the respective first and second flow paths such that, at least in a region of the sheet means, the flow of the fluids is essentially laminar and stable interfaces are formed at or in the apertures of the sheet means at said interface position, with a significant component of fluid flow of each fluid immediately adjacent the interface,
• permitting diffusive transfer of at least 1% of a total amount of said entity that may be transferred, and
• flowing the fluids towards and away from the region of the sheet means in their respective flow paths without mixing of the fluids.